We have developed a sensitive HPLC method for quantitation of polysaccharide (PS) in Hib conjugate vaccines. The HPLC method is based on the separation of the single subunit of Hib PS from many other components in a NaOH-treated vaccine by high-performance anion-exchange chromatography using a Dionex CarboPac PA1 column. The PS subunit in column eluate was detected and quantified using a newly developed Dionex Electrochemical Detector, ED40. This method could detect as low as 0.125 mg/mL of Hib PS in a vaccine. This method has been successfully used to determine the PS content of combination vaccines such as Lederle's Tetracel and Tetramune and Merck's COMVAX, in which Hib conjugates are one of active vaccine components. Preliminary results indicated that the HPLC method could also be used to quantitate the percentage of Hib conjugates adsorbed onto alum, an adjuvant, in these vaccines.